1. Field of the Invention
This invention relates to an apparatus for transferring an article to a predetermined location by converting rotational movement to linear movement.
2. Description of the Related Art
In each step of the conventional process of manufacturing semiconductor devices, a frog-leg-type or a belt-type transfer apparatus is used. This transfer apparatus transfers semiconductor wafers from a clean room to a process chamber at which a predetermined process is performed, or transfers processed wafers from the process chamber to the clean room.
The transfer apparatus is generally provided in a load lock chamber connected to the process chamber via a gate device such as a gate valve. The transfer apparatus transfers wafers from the clean room into the load lock chamber, and then to the process chamber after pressure in the load lock chamber is reduced to a vacuum value.
In a belt-type transfer apparatus, a belt with semiconductor wafers placed thereon is moved to thereby transfer the wafers. A belt transmission mechanism employed in the transfer apparatus is large, and accordingly the entire apparatus is large. Thus, a large load lock chamber and a large gate device must be used.
Frog-leg-type transfer apparatuses are disclosed, for example, in WO84/03196 (Published Unexamined Japanese Patent Application No. 60-183736) and in Published Unexamined Utility Model Application No. 60-61191. In a transfer apparatus of this type, two pairs of links are connected in series by means of coupling shafts, and a fork or the like is attached to the ends of the links. Wafers placed on the fork are transferred in the forward and backward directions by folding and unfolding the frog-like links.
This frog-leg-type transfer apparatus can be made smaller than the above-described belt-type apparatus. However, the load lock chamber employed in the frog-leg-type transfer apparatus must be larger than at least a circle formed assuming one link to be the radius, since the two pairs of coupled links are folded and unfolded to thereby transfer wafers. In addition, each link is long relative to the stroke of movement of a wafer, which requires large chambers.
Further, the frog-leg-type transfer apparatus also needs gears provided at the ends of the links for smoothly folding and unfolding the links. Those ends are inevitably thick, and hence the gate device provided at the junction of a process chamber must be made large.